Air duct riser



FIG. 1 is a top plan view of an air duct riser which incorporates our new design;

FIG. 2 is a side elevation view of the air duct riser;

FIG. 3 is a front elevation view of the air duct riser; and,

FIG. 4 is a perspective view of the air duct riser.

The rear of the air duct riser is a mirror image of the front, and the bottom is a mirror image of the top. 

The ornamental design for an air duct riser, as shown and described. 